Hydraulic control apparatus

ABSTRACT

A hydraulic control apparatus includes rotatable input and output members (32, 36), relative rotation of which supplies presurized fluid from a fluid pressure source (16) to a working chamber of a hydraulic actuator (44). The members are arranged coaxially end-to-end and each member defines a transverse slot (74, 76) confronting a similar slot on the other member. A resilient member (80, 82) is received in the transverse slots and engages both input and output members to substantially prevent rotational slack therebetween.

The invention relates to a hydraulic control apparatus. Moreparticularly, the invention relates to an improvement to hydrauliccontrol apparatus of the type having coaxially arranged rotatable inputand output members which are received in the bore of an elongatedrotatable sleeve member. The members define axially extending grooveswhich in registry cooperate to define an axially extending aperture atthe interface of the members. An elongated pin is received in theaxially extending aperture so that the members are coupled for rotationin unison. The axially extending grooves in the sleeve and outputmembers cooperate to define an aperture substantially coinciding to thecross section of the pin. Consequently, the pin substantially preventsrelative rotation of the sleeve and output members. The axiallyextending groove in the input member is circumferentially enlarged sothat the input member has a limited rotational freedom relative thesleeve and output members. The sleeve and input members have aperturesand recesses which cooperate to define a pair of fluid flow paths.Relative rotation of the sleeve and input members causes an increasedresistance to fluid flow in one path and a decrease in the fluid flowresistance of the other path. As a result, the hydraulic controlapparatus may be used to control the supply of pressurized fluid to anactuator assisting rotation of the output member in response to rotationof the input member. The axially-extending groove defined by the inputmember and the pin cooperate to define reaction chambers connected tothe fluid flow paths so that pressurized fluid in the reaction chamberscauses a torque resisting relative rotation of the sleeve and inputmembers. Additionally, a centering spring carried by the input memberbiases the sleeve and input member to a neutral relative positionwherein the resistances to fluid flow are substantially equal in the twofluid flow paths.

A power assistance control device is known in accordance with the U.S.Pat. No. 4,057,079 (hereinafter "079"), issued Nov. 8, 1977 to AlistairG. Taig, the disclosure of which is incorporated herein by reference tothe extent necessary for a complete understanding of the presentinvention, wherein a part analogous to the elongated pin described aboveis defined by a cylindrical slug. The shape of the axially extendinggroove in the input member is such that the input member and slugcooperate with the output member to define a double restriction in eachof the two fluid flow paths of the device. As a result, the controldevice has a nonlinear or two-slope operating characteristic of actuatorpressure versus input torque. The cylindrical slug is slidably receivedin the axially extending aperture so that the quality of fit between theinput and output member and slug effects at least one of the flow pathrestrictions. Specifically, the radial clearance between the slug andthe input member defines a leakage path between the reaction chambers.The leakage path effects at least one of the fluid flow pathrestrictions. Consequently, precise dimensional tolerances must bemaintained during manufacturing of the device in order to minimize theleakage path.

An improved hydraulic control apparatus is known in accordance with theU.S. Pat. No. 4,117,864, (hereinafter "864") entitled, Power SteeringControl Valve, issued Oct. 3, 1978 to A. G. Taig wherein a partanalogous to the elongated pin described above is defined by areleasable projection on the sleeve member. The releasable projection isbiased radially outwardly into the axially extending groove on thesleeve member by a pair of resilient snap rings. The snap ringssubstantially prevent relative movement of the sleeve member andprojection so that the leakage path defined between the input member andprojection is not varied by radial movement of the projection.Nevertheless, precise dimensional tolerances must be maintained duringmanufacturing of the apparatus in order to control the fluid flowrestrictions. Further, the sleeve member and the output member arecoupled for rotation in unison by the releasable projection on thesleeve member. Slack, lost motion, or relative rotational freedom of thesleeve and output member results unless precise tolerances aremaintained in manufacturing of the apparatus. Additionally, a centeringspring is defined by a pair of leaf springs which are received in atransverse bore defined by the input member. The leaf springs extendradially outwardly from the bore and engage the radial walls of anaxially extending groove defined by the sleeve member. The leaf springsmust contemporaneously engage both the input member and the sleevemember in order to prevent lost motion between the input and sleevemembers. Consequently, precise control of the shape of the leaf springsand of the dimensions of the bore and groove on the input and sleevemembers, respectively, must be maintained. Further, the spring-receivinggrooves in the sleeve member weaken the sleeve member. Additionally, oneof the input and output members includes an axailly extendingprojection. The other of the input and output members defines a blindbore rotatably receiving the projection. Consequently, the projectionand blind bore cooperate to define a pilot bearing for the input andoutput members.

It will be appreciated in light of the above that variations of theoperating characteristic of the apparatus, as well as slack in theconnection between the input and output members, are the result of afailure to maintain precise manufacturing tolerances throughout thecontrol apparatus according to the "079" and "864" patents. Variationsof the operating characteristic of the apparatus or slack between theinput and output members is, more likely than not, unacceptable;particularly when the hydraulic control apparatus is employed in a powersteering unit for a vehicle. Further, the apparatus illustrated in the"079" and "864" patent have recesses in the sleeve and input memberswhich cooperate to define the pair of flow paths. The recesses must beprecisely positioned relative to each other so that the fluid flowrestrictions of the two flow paths are balanced in the neutral positionof the valve. In order to manufacture the input and output membersaccording to the "079" and "864" patents with sufficient precision tomake the apparatus operate properly, expensive electric-dischargemachining (EDM) or electro-chemical machining (ECM) processes arenecessary.

Accordingly, it is an object of the invention to provide a hydrauliccontrol apparatus which avoids one or more of the shortcomings of priorapparatus of the type described above.

A hydraulic control apparatus according to the invention includes inputand output members which each define a transverse slot adjacent theother member. The transverse slots in registry cooperate to define atransverse aperture. A pair of leaf springs are received in thetransverse aperture with the width of each spring disposed parallel tothe axis of the input and output members. As a result, approximatelyone-half of the width of each leaf spring is received by each of theinput and output members. Because the transverse slots are of thesubstantially same width, the leaf springs contemporaneously engage boththe input and output members to substantially eliminate slack or lostmotion between the input and output members. Additionally, because thesleeve member does not have axially extending grooves for receiving thecentering spring, a sleeve member according to the invention istorsionally stronger than a sleeve member according to the "864"invention.

A hydraulic control apparatus according to the invention includes asleeve member having an axially extending groove for receiving anelongated pin. The axially extending groove includes radially extendingparallel walls. The portion of the elongated pin which is received inthe groove of the sleeve member includes surfaces which aresubstantially parallel and which slidably engage the walls of theaxially extending groove. The sleeve member groove and elongated pincooperate to define a pressure chamber. A passage communicatespressurized fluid from the reaction chambers to the pressure chamber sothat the elongated pin is biased radially inwardly into engagement withthe input member by the pressurized fluid. Consequently, the leakagepath defined between the elongated pin and input member of prior controlapparatus is not present in the invention.

Further, an apparatus according to the invention includes an inputmember with a pair of recesses disposed on opposite sides of the axiallyextending groove. The recesses include radially extending surfaces whichare parallel. Consequently, the recesses may be formed by plunge-cuttinginto the input member with a pair of spaced apart milling cutters.Because the spacing of the milling cutters may be easily controlled withgreat precision, the location of the parallel surfaces on the inputmember is easily controlled. The edges formed by the intersection of theparallel surfaces with the outer surface of the input member cooperatewith the recesses in the sleeve member to define variable-arearestrictions in the pair of flow paths. Because the locations of theedges on the input member are precisely controlled, the balancing of theflow restrictions defined in the two flow paths when the input andsleeve member are in the neutral position is more easily achieved in anapparatus according to the invention than in prior apparatus.

The advantages offered by the invention are mainly that the centeringspring is carried between the input and output members so that lostmotion between the members is eliminated; lost motion between the sleevemember and the output member is not realized as lost motion between theinput and output members; the input and output members cooperate via thecentering spring and elongated pin to define a universal joint so thatangular misalignment of the members is accommodated without adverselyeffecting the operation of the apparatus; consequently, a pilot bearingis not needed between the input and output member; the elongated pin ishydraulically biased radially inwardly into engagement with the inputmember so that the leakage path defined in prior apparatus by the radialclearance of the pin and input member is absent from the invention; therecesses on the input member include parallel surfaces which facilitatesthe precise formation of the valve edges on the input member withoutexpensive machining processes.

Two ways of carrying out the invention are described in detail belowwith reference to drawing figures which illustrate only these twospecific embodiments, in which;

FIG. 1 is a view schematically illustrating a hydraulic controlapparatus according to the invention partly in cross section taken alongthe line 1--1 of FIG. 2;

FIG. 2 is an enlarged cross-sectional view taken along the line 2--2 ofFIG. 1;

FIG. 3 is an enlarged view of an encircled portion of FIG. 2;

FIG. 4 is an isolated exploded assembly view of a portion of thehydraulic control apparatus;

FIG. 5 is an view similar to FIG. 3 illustrating an alternativeembodiment of the invention; and

FIG. 6 is an isolated exploded assembly view of a portion of thealternative embodiment of the hydraulic control apparatus.

With reference to FIG. 1, a rack-and-pinion power steering gear for anautomotive vehicle is generally referenced at 10. The steering gear 10embodies a hydraulic control apparatus 12 according to the presentinvention. The housing 14 of the power steering gear 10 communicateswith a constant flow fluid pressure source 16, such as a power steeringpump on a vehicle (not shown). The fluid pressure source 16 iscommunicated with a stepped bore 18 within the housing 14 via a conduit20 and an inlet 22 on the housing 14. An outlet 24 returns fluid fromthe housing 14 to a reservoir of the fluid pressure source 16 via aconduit 26. The reservoir of the fluid pressure source is vented to theatmosphere, for example, via a vented filler cap 28 on the reservoir ofthe power steering pump 16.

An annular plug 30 is received in the stepped bore 18. The plug 30journals an input member 32 which extends outwardly of the housing 18.The input member 32 terminates in a splined end 34 by which the inputmember is coupled for rotation in unison with the steering wheel (notshown) of the vehicle. An output member 36 is journaled in the housing14 via a pair of ball bearings 38. The output member 36 defines a piniongear at 40 which drivingly engages the rack 42. A pair of tie rods (notshown) connect the rack 42 to the dirigible wheels of the vehicle sothat translation of the rack 42 in response to rotation of the outputmember 36 steers the vehicle. The hydraulic control apparatus 12 couplesthe input and output members for rotation in unison and suppliespressurized fluid to a double acting hydraulic cylinder or actuator 44via conduits 46 and 48. The actuator 44 assists translation of the rack42 in response to rotation of the input member 32.

In accordance with the invention, the hydraulic control apparatus 12includes a sleeve member 50 which is rotatably received in the steppedbore 18 of the housing 14. The sleeve member 50 carries fourspaced-apart sealing members 52 which sealingly cooperate with thehousing 14 to define three annular chambers 54, 56 and 58. The chamber54 receives pressurized fluid via the conduit 20 while chambers 56 and58 communicate with the working chambers of the actuator 44. The sleevemember 50 defines a bore 60 receiving the input and output members 32and 36, respectively. Upon inspection of FIG. 4, it will be seen thatthe input member 32 and a radially extending flange 62 on the outputmember 36 defines circumferentially aligning grooves 64 and 66,respectively. The grooves 64 and 66 oppose an axially extending groove68 on the sleeve member 32. In registry, the grooves 64, 66, and 68cooperate to define an axially extending aperture 70, viewing FIG. 2. Arectangular pin 72 is received in the aperture 70 defined by the grooves64, 66 and 68 so that the input, output, and sleeve members are coupledfor rotation in unison.

Turning to FIGS. 2 and 3, it will be seen that the groove 64 on inputmember 32 is circumferentially enlarged so that the input member has alimited rotational freedom relative the sleeve and output member.

Further, the input and output members 32 and 36 define a pair ofradially extending transverse slots 74 and 76, respectively, viewingFIG. 4. The slots 74 and 76 extend axially relative the input and outputmembers and cooperate in registry to define a transverse aperture 78,viewing FIG. 1. A pair of opposed leaf springs 80 and 82 are received inthe aperture 74 in back-to-back relationship. The springs 80 and 82engage each other and a point 84. Further, the springs 80 and 82 includeends 86 and 88 which are resiliently biased circumferentially away fromeach other because the springs are distorted in the aperture 78. Each ofthe input and output members receives approximately one-half the widthof each spring, viewing FIGS. 1 and 4. Because the slots 74 and 76 aresubstantially equal in width, the springs 80 and 82 engage both theinput and output members contemporaneously so that rotational slack iseliminated from the apparatus. The springs 80 and 82 bias the input andoutput members to a neutral relative position.

Viewing FIGS. 2, 3, and 4, it will be seen that the sleeve member 50includes a pair of axially extending recesses 87 and 89 which areadjacent the pin 72. The recesses 87 and 89 no not open axially at theends of the sleeve member. A pair of radial bores 90 and 92 defined inthe sleeve member connect the recesses 87 and 89 to the conduits 46 and48, respectively, via the annular chambers 56 and 58. The input member32 defines a pair of axially extending recesses 94 and 96 which do notopen axially at the ends of the input member. A portion 98 of each ofthe recesses 94 and 96 is parallel to the portion 98 of the otherrecess. A pair of radial bores 100 and 102 are defined by the sleevemember 50. The bores 100 and 102 connect the recesses 94 and 96 to theinput conduit 20 via the annular chamber 54. The input, output andsleeve members cooperate with the pin 72 to define a pair of pressurecommunication and fluid flow paths from the inlet 22 and annular chamber54 to the conduits 46 and 48. One communication path is defined by thebore 100, recess 94, recess 87, bore 90 and chamber 56. The othercommunication path is defined by the bore 102, recess 98, recess 89,bore 92, and chamber 58. The surfaces 98 cooperate with the recesses 87and 89 to define a pair of variable-area flow restrictions in thecommunication paths. Additionally, both communication paths communicatewith an annular chamber 104 defined in the housing 14 because theaxially extending groove 64 in the input member 32 opens axially at theends of the input member. The annular chamber 104 communicates with theoutlet port 24.

Upon inspection of FIG. 3, it will be seen that the pin 72 and inputmember 32 cooperate to define reaction chambers 106 and 108 in thegroove 64. The reaction chambers 106 and 108 communicate with therecesses 87 and 89, respectively. Further, the portion of pin 72 whichis received in the groove 68 defines surfaces 110 which aresubstantially parallel. The radially-extending walls of the groove 68are also substantially parallel so that the pin 72 is movable radiallyin the groove 68. Sleeve member 50 and pin 72 cooperate to define achamber 112. A bore 114 extends radially through the pin 72 and connectsthe reaction chambers 106 and 108 to the chamber 112. The input member32 includes a radially raised, axially extending abutment 116 in thegroove 64. The abutment 116 engages the pin 72 at a surface 118 on theabutment. Surface 118 defines a radius with respect to the axis of theinput member 32.

Turning now to FIGS. 1 and 4, it will be seen that the bore 60 of sleevemember 50 is stepped to provide a shoulder 120. The ends 86 and 88 ofthe leaf springs 80 and 82 define notches 122 which receive a wireretaining ring 124. The pin 72 defines a radially extending notch 126.The notch 126 receives the retaining ring 124 which is engageable withthe shoulder 120. Consequently, the ring 124 retains the springs 80 and82 and pin 72 in the aperture 78 and 70, respectively, while allowingradial movement of the pin 72.

An alternative embodiment of the invention is illustrated by FIGS. 5 and6. In order to obtain reference numerals for use in FIGS. 5 and 6,features which are analogous in structure or function to thoseillustrated in FIGS. 1-4 are referenced by the numeral used in FIGS. 1-4and increased by 200. The embodiment of the invention illustrated byFIGS. 5 and 6 is substantially the same as the embodiment illustrated byFIGS. 1-4, with the exception of features to be hereinafter explained.

Upon inspection of FIG. 5 it will be seen that the pin 272 defines anarcuate surface 130 which slidably engages the surface 318 of abutment316. Because of the arcuate surface 130 of pin 272, the cross-sectionalarea of the leakage path defined by groove 264 between the recesses 287and 289 and the chamber 304 is increased as compared to the embodimentillustrated by FIGS. 1-4. As a result, the operating characteristic ofactuator pressure versus input torque of the two embodiments of theinvention are different. Those skilled in the art will recognize thatthe operating characteristic of the invention may be varied by changingthe curvature of the arcuate surface 130 so that the cross section ofthe leakage path from recesses 287 and 289, to the reservoir via groove264 and chamber 304 is varied.

FIG. 6 illustrates a retaining ring 132 which is generally S-shaped. Thesleeve member 250 defines an annular groove 134. Similarly, the inputmember defines an annular groove 136. A circumferentially extendingaperture 138 is defined by the pin 272. The retaining ring 132 isreceived by grooves 134 and 136 and by the aperture 138. Consequently,the pin 272 is retained axially relative the input and sleeve member andthe input member 232 sleeve member 250, pin 272 and ring 132 comprise aunitary assembly for installation in the housing 14.

When a steering input is effected by a vehicle operator via the steeringwheel (not shown), the input member 32 (232) is moved rotationallyrelative the sleeve member 50 (250) (parenthetical references to FIGS. 5and 6 will be hereinafter omitted and considered subsumed in thereference numeral used in FIGS. 1-4, where appropriate). For example, ifthe input member 32 is rotated clockwise relative the sleeve member 50,the surfaces 98 cooperate with the recesses 87 and 89 so that therestriction between recesses 96 and 89 is opened and the restrictionbetween recesses 94 and 87 is closed. At the same time, the leakage pathfrom the recess 89 to the chamber 104 via groove 64 is reduced while theleakage path from recess 87 to chamber 104 via groove 64 is opened. As aresult, pressurized fluid is communicated to the recess 89 and to oneworking chamber of the actuator 44 to effect a right-hand turn of thevehicle. The other working chamber of the actuator is vented to thereservoir via the leakage path from recess 87 to chamber 104.Pressurized fluid is communicated from recess 89 to reaction chamber108, producing a reaction torque on the input member 32 which opposesrotation of the input member 32 relative sleeve member 50. The reactiontorque produced on the input member 32 is proportional to actuatorchamber pressure. Additionally, pressurized fluid is communicated fromreaction chamber 108 to chamber 112 via the radial bore 114.Consequently, the pin 72 is biased radially inwardly into engagementwith the input member 32. Clockwise relative movement of the abutment116 relative bore 114 substantially closes communication of the reactionchamber 106 with the bore 114 so that leakage between the reactionchambers 106 and 108 is substantially prevented.

Of course, the input member 32 is movable counter clockwise relative thesleeve member 50 to effect a left-hand turn, in which case the functionsof the recesses and reaction chambers are reversed.

I claim:
 1. Apparatus having relatively rotatable input and outputmembers arranged coaxially end-to-end and means for resiliently biasingsaid members to a neutral relative rotational position, characterized inthat each of said members defines a radially extending transverse slotadjacent the other member, said slots in registry cooperating to definea transverse aperture, said biasing means being received in saidtransverse aperture, said transverse slots extend axially substantiallyequal distances relative said members, said biasing means includes atleast one elongated resilient leaf spring received in said transverseaperture with the width of said leaf spring extending axially so thatsubstantially one-half the width of said leaf spring is received in eachof said transverse slots, said biasing means includes a pair ofsubstantially similar leaf springs received in said transverse aperturein back-to-back relationship, said leaf springs engage one another at apoint which is substantially coincident with the axis of said members,said slots including axially extending walls, said leaf springsincluding ends extending radially and contemporaneously engaging theaxially extending walls of said slots, and said leaf springs terminatein radially outer edges defining radially extending notches, saidnotches receiving a retaining ring.
 2. The invention of claim 1 whereinsaid members define circumferentially aligned grooves, said groovesreceiving an elongated pin coupling said members for rotation in unison.3. The invention of claim 2 wherein said elongated pin defines aradially extending groove receiving said retaining ring.
 4. Theinvention of claim 2 wherein said transverse slots are disposedsubstantially perpendicularly relative said circumferentially alignedgrooves.
 5. The invention of claim 1 wherein said members definecircumferentially aligned grooves, said apparatus further including asleeve member receiving said members and said sleeve member defining agroove opposing the grooves of said input and output members, saidgrooves cooperating to define an axially extending aperture receiving anelongated pin coupling all of said members for rotation in unison. 6.The invention of claim 5 wherein said axially extending aperture isdisposed substantially perpendicularly relative said transverse slots.7. The invention of claim 5 wherein one of said input and sleeve membersdefines a radially extending annular groove disposed toward the other ofsaid input and sleeve members, said elongated pin defining acircumferentially-extending aperture, said apparatus including asubstantially S-shaped retaining ring, said circumferentially extendingaperture and said annular groove receiving said retaining ring.
 8. Theinvention of claim 7 wherein both of said input and sleeve membersdefine radially extending annular grooves disposed toward the other ofsaid input and sleeve members, both of said annular grooves receivingsaid retaining ring whereby said input and sleeve members, saidelongated pin and said retaining ring comprise a unitary assembly.